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United States Patent |
5,702,471
|
Grundei
,   et al.
|
December 30, 1997
|
Finger joint
Abstract
A finger joint has first and second hollow anchorage shafts (2, 3) which
can be implanted in finger tubular bones with a hinge joint (4) arranged
between them. The first hollow shaft (2) can be connected with a ball cage
(5) of the hinge joint (4) in which a spherical part (6) is mounted, on
which a protruding stem (7) is formed. This stem (7) passes through the
ball cage (5), and indeed through a slit (8) provided therefor in the wall
of the ball cage (5). The slit (8) in the ball cage (5) widens
continuously from the point (P) at which the stem (7) passes through the
ball cage (5) in the extended position of the joint (4) to the point (M)
at which the stem (7) passes through the ball cage (5) in the flexed
position of the joint. In this manner, additional play is allowed to the
joint in the flexed position, which largely corresponds to the
physiological coordinated movement of a finger joint.
Inventors:
|
Grundei; Hans (Lubeck, DE);
Rudigier; Jurgen (Offenburg, DE);
Weber; Christian (Hohwald, DE)
|
Assignee:
|
ESKA Medical GmbH & Co. (Lubeck, DE)
|
Appl. No.:
|
617231 |
Filed:
|
March 18, 1996 |
Foreign Application Priority Data
| Apr 06, 1995[DE] | 195 12 854.0 |
Current U.S. Class: |
623/21.16; 403/115 |
Intern'l Class: |
A61F 002/42 |
Field of Search: |
623/21,20,18
403/114-116
|
References Cited
U.S. Patent Documents
3196463 | Jul., 1965 | Farneth | 403/114.
|
3638243 | Feb., 1972 | Campbell, Jr. et al.
| |
3851979 | Dec., 1974 | Becker | 403/115.
|
4064568 | Dec., 1977 | Grundei et al. | 623/20.
|
4276660 | Jul., 1981 | Laure.
| |
4304011 | Dec., 1981 | Whelan.
| |
5147386 | Sep., 1992 | Carignan et al.
| |
Foreign Patent Documents |
2 651 119 | Mar., 1991 | FR.
| |
21 46 253 | Mar., 1973 | DE.
| |
25 22 377 A1 | Nov., 1976 | DE.
| |
3433263 | Mar., 1986 | DE | 623/20.
|
195 12 854 C1 | Aug., 1996 | DE.
| |
7311107 | Jan., 1975 | NL | 623/18.
|
1567200 | May., 1990 | SU | 623/20.
|
Primary Examiner: Willse; David H.
Attorney, Agent or Firm: Panitch Schwarze Jacobs & Nadel, P.C.
Claims
We claim:
1. A prosthetic finger joint (1) comprising a first and a second hollow
anchorage shaft (2, 3) configured to be implanted in tubular finger bones,
and a hinge joint (4) in a form of a ball-and-socket joint arranged
between the shafts (2,3), the first hollow shaft (2) being connected with
a ball cage (5) of the hinge joint (4), a spherical part (6) provided with
a protruding stem (7) being mounted in the ball cage, the stem (7) passing
through a slit (8) in the ball cage (5) and connecting with the second
hollow shaft (3), the slit (8) in the ball cage (5) continuously widening
from a point (P) at which the stem (7) passes through the ball cage (5) in
an extended position of the joint (4) to a point (M) at which the stem (7)
passes through the ball cage (5) in a flexed position of the joint (4).
2. The prosthetic finger joint according to claim 1, wherein the ball cage
(5) itself is a sphere, and the slit (8) penetrates through a wall of the
spherical ball cage (5) on part of a meridian from a pole (P) up to
approximately the equator.
3. The prosthetic finger joint according to claim 1, wherein the spherical
part (6) is constructed as one piece with the stem (7) and is provided
with a polyethylene coating (9).
4. The prosthetic finger joint according to claim 1, wherein a pole cap
(10) of at least a diameter of the spherical part (6) is provided, whereby
the pole cap (10) can be screwed onto the ball cage (5) as a cover to
complete a spherical outer configuration of the ball cage (5).
5. The prosthetic finger joint according to claim 1, wherein the stem (7)
extends into a sliding sleeve (11) which is connected with the second
hollow shaft (3) in such a way that the stem (7) can slide lengthwise to
execute longitudinal compensatory movements in the sleeve (11).
6. The prosthetic finger joint according to claim 5, wherein the sliding
sleeve (11) comprises polyethylene.
7. The prosthetic finger joint according to claim 5, wherein the sliding
sleeve (11) has a collar (12) on its end facing the ball cage (5), the
collar (12) lying on an exterior of the ball cage in an assembled stage of
the joint.
8. The prosthetic finger joint according to claim 7, wherein the collar
(12) is constructed as a partial spherical segment corresponding to a
spherical surface of the ball cage (5).
Description
FIELD OF THE INVENTION
The invention concerns a prosthetic finger joint. It can be implanted
following resection of a metacarpophalangeal joint between the bones of
the hand and the finger bones, as well as of an intraphalangeal joint
between the finger bones.
1. Background Of The Invention
In most cases, finger joints are resected when they are rheumatic and cause
the patient great pain. Hitherto a so-called Swanson joint has been
substituted for the natural joint, in connection with which, however, it
is not a question of a genuine joint, but rather of a silicone substitute
with two elongated anchors capable of being implanted into the tubular
bones and which are connected with a foundation of silicone. The
flexibility of silicone offers the patient a certain mobility of the
finger treated. However, the formation of a connective tissue capsule
around this "joint" has been observed, with the use of the Swanson joint,
which is detrimental for the mobility and the permanency of the Swanson
joint remaining in situ.
2. Summary Of The Invention
Against this background, it is an object of the present invention to create
an endoprosthetic finger joint which achieves a great exactitude in
imitating the natural physiological movement of a natural finger joint. In
addition to this, the preconditions for the greatest wearing comfort
possible for the patient should be created, in order to attain the widest
acceptance possible.
This object is solved by a finger joint having first and second hollow
anchorage shafts which can be implanted in tubular finger bones with a
hinge joint between them in the form of a ball and socket joint, the first
hollow shaft being connected with a ball cage (socket) of the hinge joint
and a spherical part (ball) provided with a protruding stem being mounted
in the ball cage. The protruding stem passes through a slit in the ball
cage and connects with the second hollow shaft, such that the slit widens
continuously from a pole point at which the protruding stem passes through
the ball cage in an extended position of the joint to an equatorial point
at which the protruding stem passes through the ball cage in a flexed
position of the joint. Further advantageous refinements become apparent
from the subclaims.
Accordingly, it is first of all proposed that the finger joint have a first
and a second anchorage shaft which can be implanted in the tubular bones
of the fingers or hand between which a hinge joint is arranged. The
aforementioned anchorage shafts are advantageously constructed of an
open-meshed grid network, preferably of metal, through which trabeculae
can grow and thus assure a permanent anchorage of the shafts in the bone.
The first shaft is connected with a ball cage of the hinge joint in which
is situated a spherical part provided with a stem, whereby the stem passes
through the ball cage through a slit provided in it and stands in
connection with a second hollow shaft. The slit in the ball cage widens
from the point at which the stem passes through the ball cage in the
extended position of the joint to the point at which the stem passes
through the ball cage in the flexed position.
The ball and socket joint accordingly allows not only the usual bending
movement of a hinge joint from the extended to the flexed position, but
augments play with increasing flexion of the joint, and to be sure in the
plane standing perpendicular to the plane of bending. This corresponds
approximately to the coordinated movement of a natural finger joint. The
significance of the most exactly recreated physiological coordinated
movement lies chiefly in the fact that the soft parts surrounding the
joint, such as the connective tissue and tendons, can exercise their
functions in a practically unchanged environment following implantation in
comparison with the natural state. Patient wearing comfort is hereby
increased, and acceptance of the implant promoted by this.
The connection of the hinge joint with the two hollow shafts situated in
the bones takes place preferably through conical compression connections
which have been known in the area of implantation technology for a long
time.
In accordance with a preferred specific embodiment, the ball cage is itself
a sphere. The aforementioned slit, through which the stem of the spherical
part extends, penetrates the wall of the now spherical ball cage on a
section of a meridian from one pole to approximately the equator of the
sphere. By constructing the ball cage in the shape of a sphere, there
results a compact implant which makes possible the problem-free guidance
of tendons, etc. over the ball surface in the implanted state of the
finger joint. This leads to a sparing treatment of the soft parts and
tendons of the fingers and, as a consequence of this, to a high tolerance
of the implant.
In order to obtain the highest possible tolerance and, by way of example,
to prevent metallosis, the inner spherical part is constructed in one
piece with the above-mentioned stem and provided with a polyethylene
coating, in accordance with an advantageous further development.
Preferably, the entire spherical part is coated with polyethylene. Above
and beyond this, it is likewise advantageous to coat the aforementioned
stem in the projection area at the spherical part with polyethylene in the
region in which it passes through the wall of the ball cage. A metal-metal
contact is consequently effectively avoided if the implant is made of
metal.
In case, despite all precautions, it should nonetheless become necessary to
perform a revision intervention so that the spherical part may be
exchanged, a pole cap of at least the size (diameter) of the spherical
part is provided, which can be screwed onto the ball cage in the manner of
a cover, and whose external spherical configuration completes the sphere,
according to an advantageous further development. The very compact unit
may thus be taken apart by unscrewing the pole cap from the ball cage,
whereupon the spherical part can then be removed with the projecting stem.
A new part consisting of spherical part and stem can be installed in a
simple manner, and the pole cap can be closed again.
The action of the finger joint according to the invention can be further
increased. For this it should, however, be noted in advance that it
involves not only exclusively a bending movement with the above-mentioned
enlargement of play as with the natural finger joint. A longitudinal
extension also takes place. Thus, the natural tendons are placed under
more traction during bending of the natural joint than is the case in the
extended position of the finger. In order to compensate for these changes
in length, it is provided in accordance with an advantageous further
development that the stem on the spherical part of the finger joint
extends quasi-telescopically into a sliding sleeve, which can be connected
with the above-mentioned second hollow shaft in such a way that the stem
can slide longitudinally in the sleeve. In this way, the stem can move by
sliding to compensate for the changes in length and thus provide a
compensating movement.
The sliding sleeve also preferably comprises polyethylene. It can be
permanently connected with the second hollow shaft through a conventional
conical compression joint.
The sliding sleeve preferably has a collar at its end facing the ball cage,
the collar lying on the exterior of the ball cage in the assembled state
of the joint. An at least partial covering of the slit through the wall of
the ball cage is hereby achieved. Of course, this can best be achieved in
the case where the ball cage is also itself a sphere on the exterior. Then
the collar on the sliding sleeve has a partial spherical form and can
almost completely cover the slit, so that the interior of the ball cage
remains largely free of physiological fluids, etc., which can damage the
good bearing characteristics of the joint over a long period of time.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing summary, as well as the following detailed description of a
preferred embodiment of the invention, will be better understood when read
in conjunction with the appended drawings. For the purpose of illustrating
the invention, there is shown in the drawings an embodiment which is
presently preferred. It should be understood, however, that the invention
is not limited to the precise arrangements and instrumentalities shown. In
the drawings:
FIG. 1 shows all parts of the finger joint according to the invention in a
non-assembled (exploded) state and partially in section, while a view into
the ball cage in the direction of the arrows A--A in FIG. 1 is shown in
FIG. 1a; and
FIG. 2 is a sectional view through the assembled finger joint in the flexed
position.
In the drawings, the same reference symbols refer to the same parts.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
The ball cage 5 of the hinge joint 4 is the core piece of the finger joint
1 of the invention. In the present case, the ball cage 5 is spherically
constructed and is completed in its spherical form by means of the pole
cap 10. For this purpose, the thread 16 on the pole cap 10 can be screwed
into the internal thread 17 of ball cage 5.
Protruding radially from the pole cap 10 is tapered cone 15 which can be
connected permanently, but also separably, with a conical fitting sleeve
14 in the first hollow shaft 2 by means of a conical compression
connection. In the present case, hollow shaft 2 consists of an open-meshed
grid network, through which bone trabeculae of the spongiosa surrounding
the shaft 2 can grow in for a permanent fixation of the implant following
implantation.
The wall of the ball cage 5 is penetrated in the area from its pole P to
its equator region M by a guiding slit 8. This guiding slit 8 widens
continuously from the area around the pole P down to the equatorial area M
of the ball cage 5, as can be clearly recognized in FIG. 1a. Through this,
a greater play in the flexed position of the finger joint in the direction
of the double arrow in FIG. 1a is allowed to stem 7, which is formed as an
extension on the spherical part 6 (FIG. 1), than is the case with the
extended finger joint, where the play is practically equal to zero. This
largely corresponds to the physiological coordinated movement of a natural
finger joint.
In the present case, the spherical part 6 is coated with a polyethylene
layer 9 which also covers the lower region of the projecting stem 7 and,
to be sure, to such an extent that no contact can take place between the
(metal) stem 7 and the (metal) ball cage 5 in the area of the slit 8. A
metallosis is hereby effectively prevented.
A second hollow shaft 3 is provided which, in the present case, is
constructed exactly like the first hollow shaft 2, thus consisting of an
open-meshed grid network and having a conical fitting sleeve 13. A sliding
sleeve 11 can be brought into a conical compression connection with the
conical fitting sleeve, the sliding sleeve having for this purpose the
external contours of a tapered cone. The sliding sleeve 11 is, however,
constructed cylindrically on the interior in such a way that the stem 7 is
mounted so that it can slide longitudinally in sliding sleeve 11. In this
way, a quasi-telescopic motion of the stem within sliding sleeve 11 is
also made possible in the direction of the double arrow in FIG. 1
following implantation of the finger joint, by means of which
longitudinally compensatory movements can be executed.
In the present case, the sliding sleeve 11 has a collar 12 on its end
facing the ball cage 5 of the hinge joint 4. The ball cage 5 is here
constructed in the form of a sphere, and the collar 12 lies on the outside
of the ball cage 5 in the assembled state of the finger joint (FIG. 2).
Here the collar 12 is to be seen as part of a spherical segment. The
collar 12 serves to at least partially cover the slit 8, through which the
stem 7 passes, in order to avoid a penetration by physiological fluids
such as blood etc. into the interior of the ball cage. The collar 12 can
be basically larger in concrete embodiments than as shown in the drawings.
The embodiment depicted permits, as is apparent from FIG. 2, a bending
movement of up to 90.degree.. The finger joint of the invention is not,
however, restricted to this dimension. A bending range of 100.degree., for
example, is also possible by lengthening the slit.
Assembly of the parts from FIG. 1 takes place in an intuitive manner by
inserting the spherical part with stem 7 into the ball cage 5, after which
the stem 7 protrudes through the slit 8. Thereafter the pole cap 10 is
screwed onto the remaining ball cage 5. The sliding sleeve 11 is slipped
over the stem 7 until the collar 12 lies on the outer wall of the ball
cage. After that, the conical compression connections are made between the
fitting sleeve 14 in hollow shaft 2 and the tapered cone 15 on the pole
cap 10, on the one hand, and between the conical fitting sleeve 13 in
hollow shaft 3 and the conical tapered cone which is formed as an
extension on the exterior of the sliding sleeve 11.
It will be appreciated by those skilled in the art that changes could be
made to the embodiment described above without departing from the broad
inventive concept thereof. It is understood, therefore, that this
invention is not limited to the particular embodiments disclosed, but it
is intended to cover modifications within the spirit and scope of the
present invention as defined by the appended claims.
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